1. Field of the Invention
The present invention relates generally to an electric oven, and more particularly, to an electric oven that has at least two broil heaters and a method for preheating an electric oven capable of reducing the preheating time by using one or more of the two broil heaters.
2. Description of Related Art
In general, an electric oven is a cooking appliance for heating food with dry heat, particularly after sealing the food in the cooking appliance. The dry heat may be provided using various kinds of heaters including a ceramic heater, a sheath heater, a halogen heater, and a high frequency generator (microwaves) that are operated by electricity. The electric oven has a fast cooking speed and high thermal efficiency since it heats both inside and outside of the food at the same time and is safer than gas or wood burning appliances because it is operated by electricity. Therefore, there is a trend that the electric oven is being increasingly used.
FIG. 1 is a perspective view illustrating a conventional electric oven. The electric oven 1 has an oven body 10 having a generally hexahedral shape and a cooking chamber 20 formed therein for receiving food and cooking food. Both side surfaces of the oven body 10 defining an external shape of the oven body 10 are provided with side plates 30 where a portion of the side plate 30 is formed with a plurality of side intake holes 32. The side intake holes 32 draw in external air to cool the surface of the oven body 10 and components inside the oven body 10.
The oven body 10 also includes a rear surface formed from a rear plate 40 and a front surface formed from a front plate 36. The front plate 36 includes an opening that accesses the cooking chamber 20. An oven door 50 is provided to selectively open and close the cooking chamber 20. The oven door 50 has a generally rectangular shape, and a lower end portion of the oven door 50 is pivotally hinged with a front lower end portion of the oven body 10, preferably at the front plate 36. Also, a door handle 52 is provided at an upper end portion of the oven door 50 to facilitate pivoting of the oven door 50 by being grasped by a user.
An upper front portion of the oven body 10 is provided with a control panel 60, in which operation knobs 62 for operating the electric oven 1, displays 64 for displaying the operation state of the electric oven 1, and the like are provided thereon. An electric parts chamber 70 is formed at a rear of the control panel 60, for example, at an upper portion of the cooking chamber 20. The electric part chamber 70 is configured to receive electric devices and components (not shown) for the operation of the electric oven 1, for example, a magnetron, a high voltage transformer, and a cooling fan assembly.
As shown in FIG. 2, three types of heaters are generally provided on or adjacent walls of the cooking chamber 20. For examples, a heater installed on the ceiling is generally referred to as a top heater 81, and a heater located in the bottom is generally referred to as a bottom heater 82. The top heater 81 may be in the form of a broil heater and the bottom heater 82 may be in the form of a bake heater. A third heater 83 located on the rear wall is generally referred to as a convection heater since it is generally installed together with a convention fan. The third heater 83 is protected by a cover 85.
These three types of heaters 81, 82 and 83 have different characteristics in relation to cooking of foods. The convection heater 83 transfers heat mainly by convection and is capable of making the temperature of the inside of the cooking chamber 20 to be uniform within a short time. The broil heater 81 is constituted of a high capacity heater as compared to the convection heater 83 and the bake heater 82, and the broil heater 81 is capable of heating food within a short time by radiant heat.
These heaters 81, 82, and 83 are operated alone or in combination with each other in correspondence to cooking modes that are preset according to characteristics of the food to be cooked. In addition, the on/off periods of the respective heaters and total heating time may also be controlled based on the preset cooking modes. Although all of the heaters 81, 82, and 83 may be operated at the same time, this generally results in too much power consumption. Also, when all the heaters are operated at the same time, the temperature of the cooking chamber is generally raised to an excessive level. For these reasons, cooking modes are preset so that the heaters are optimally used alone or in combination according to the characteristics of the food to be cooked. Further, even when the respective heaters are operated, total power consumed by the electric oven 1 is controlled to be limited to a predetermined upper limit value so that the power consumed does not exceed this upper limit.
In order to optimally cook certain types of foods, it is desirable that the inside of the cooking chamber is heater prior to placing the food in the cooking chamber 20. This is referred to as preheating, and it is desirable that the preheating time is short, but, at the same time, it is also important for cooking of the food to preheat the inside of the cooking chamber so that the inside of the cooking chamber has a uniform temperature distribution.
In order to uniformly raise the temperature of the inside of the cooking chamber, it is preferred to perform the preheating with the convection heater 83. This is because the heat generated by the convection heater 83 is rapidly transferred to the inside of the cooking chamber by the convection fan. However, since the convection heater 83 generates little heat as compared to the broil beater 81, the preheating of the cooking chamber takes a relatively long time.
While the broil heater 81 may generate more heat than the convection heater 83 and thus can complete the preheating within a short time, the preheating is limited with respect to a specific area. In particular, since the heat generated by the broil heater 81 is mostly transferred, not by convection, but by radiation, the temperature rise all over the cooking chamber 20 is low unless an object such as a food capable of absorbing the radiant heat is introduced into the cooking chamber 20. Also, since the temperature is rapidly raised only in the vicinity of the ceiling on which the broil heater 81 is located, there is a problem that the temperature distribution in the inside of the cooking chamber is not uniform. In other words, while the broil heater 81 consumes much power as it generates large amounts of heat, it has a low efficiency for heating the inside of the cooking chamber to provide uniform temperature distribution.
If the preheating is preformed using both the convection heater 83 and the broil heater 81, total power consumption may exceed maximum wattage preset in the electric oven. Therefore, the preheating is performed by using only one of the convection heater 83 or the broil heater 81, or by alternating the use of the convection heater 83 and the broil heater 81 over time. The problem with preheating by the former approach is described above. The problem with preheating by the latter approach is that one heater is naturally cooled while the other heater is operated and thus additional power and time are consumed to reheat the cooled heater.
In addition, although it is possible to operate two or more heaters, including the bake heater, at the same time, it is difficult to operate two or more heaters for a long time since the power for operating the heaters should be distributed within the limit of the maximum wattage of the electric oven. That is to say, there is a limitation in that the time for which the two or more heaters are operated at the same time is very short as compared to the total preheating time and one of the heaters should be operated in a low power level when the two heaters are operated at the same time. Therefore, even with the method described above, the preheating cannot be completed within a short time and the waste of power becomes significant.